Add a test for ELF Fileheader Flag

Also, do not print Flags value when e_flags is 0

Author: aakanksha555

llvm/include/llvm/ObjectYAML/ELFYAML.h

@@ -117,7 +117,7 @@ struct FileHeader {
   llvm::yaml::Hex8 ABIVersion;
   ELF_ET Type;
   std::optional<ELF_EM> Machine;
-  ELF_EF Flags;
+  std::optional<ELF_EF> Flags;
   llvm::yaml::Hex64 Entry;
   std::optional<StringRef> SectionHeaderStringTable;
 

llvm/lib/ObjectYAML/ELFEmitter.cpp

@@ -482,9 +482,10 @@ void ELFState<ELFT>::writeELFHeader(raw_ostream &OS) {
   Header.e_version = EV_CURRENT;
   Header.e_entry = Doc.Header.Entry;
   if (Doc.Header.Flags)
-    Header.e_flags = Doc.Header.Flags;
+    Header.e_flags = *Doc.Header.Flags;
   else
     Header.e_flags = 0;
+
   Header.e_ehsize = sizeof(Elf_Ehdr);
 
   if (Doc.Header.EPhOff)

llvm/test/tools/llvm-objcopy/MachO/remove-swift-symbols.test

@@ -112,7 +112,7 @@ FileHeader:
   filetype:        0x00000002
   ncmds:           4
   sizeofcmds:      400
-  flags:           [[FLAGS=<none>]]
+  flags:           [[FLAGS]]
   reserved:        0x00000000
 LoadCommands:
   - cmd:             LC_SEGMENT_64

llvm/test/tools/obj2yaml/ELF/file-header-flags.yaml

@@ -0,0 +1,48 @@
+## Test for FileHeader Flags; when FLAGS variable isn't defined, the e_flags value is 0, otherwise it's the specified value
+
+# RUN: yaml2obj %s -o %t
+# RUN: llvm-readobj -h %t | FileCheck %s --check-prefixes=CHECK,NO-FLAG
+
+# RUN: yaml2obj %s -o %t -DFLAGS=[EF_AMDGPU_MACH_AMDGCN_GFX900]
+# RUN: llvm-readobj -h %t | FileCheck %s --check-prefixes=CHECK,FLAG
+
+!ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  OSABI:           ELFOSABI_AMDGPU_HSA
+  Type:            ET_EXEC
+  Machine:         EM_AMDGPU
+  Flags:           [[FLAGS=<none>]]
+
+# CHECK:              Format: elf64-amdgpu
+# CHECK-NEXT:         Arch: {{(unknown|amdgcn)}}
+# CHECK-NEXT:         AddressSize: 64bit
+# CHECK-NEXT:         LoadName: <Not found>
+# CHECK-NEXT:         ElfHeader {
+# CHECK-NEXT:           Ident {
+# CHECK-NEXT:             Magic: (7F 45 4C 46)
+# CHECK-NEXT:             Class: 64-bit (0x2)
+# CHECK-NEXT:             DataEncoding: LittleEndian (0x1)
+# CHECK-NEXT:             FileVersion: 1
+# CHECK-NEXT:             OS/ABI: AMDGPU_HSA (0x40)
+# CHECK-NEXT:             ABIVersion: 0
+# CHECK-NEXT:             Unused: (00 00 00 00 00 00 00)
+# CHECK-NEXT:           }
+# CHECK-NEXT:           Type: Executable (0x2)
+# CHECK-NEXT:           Machine: EM_AMDGPU (0xE0)
+# CHECK-NEXT:           Version: 1
+# CHECK-NEXT:           Entry: 0x0
+# CHECK-NEXT:           ProgramHeaderOffset: 0x0
+# CHECK-NEXT:           SectionHeaderOffset: 0x58
+# NO-FLAG-NEXT:         Flags [ (0x0)
+# FLAG-NEXT:            Flags [ (0x2C)
+# FLAG-NEXT:              EF_AMDGPU_MACH_AMDGCN_GFX900 (0x2C)
+# CHECK-NEXT:             ]
+# CHECK-NEXT:           HeaderSize: 64
+# CHECK-NEXT:           ProgramHeaderEntrySize: 0
+# CHECK-NEXT:           ProgramHeaderCount: 0
+# CHECK-NEXT:           SectionHeaderEntrySize: 64
+# CHECK-NEXT:           SectionHeaderCount: 3
+# CHECK-NEXT:           StringTableSectionIndex: 2
+# CHECK-NEXT:         }

llvm/tools/obj2yaml/elf2yaml.cpp

@@ -281,7 +281,8 @@ template <class ELFT> Expected<ELFYAML::Object *> ELFDumper<ELFT>::dump() {
   Y->Header.Type = Obj.getHeader().e_type;
   if (Obj.getHeader().e_machine != 0)
     Y->Header.Machine = ELFYAML::ELF_EM(Obj.getHeader().e_machine);
-  Y->Header.Flags = Obj.getHeader().e_flags;
+  if (Obj.getHeader().e_flags != 0)
+    Y->Header.Flags = Obj.getHeader().e_flags;
   Y->Header.Entry = Obj.getHeader().e_entry;
 
   // Dump sections